The process of making pressure-sensitive adhesive laminate wherein the face stock is die-cut involves several sequential steps. In general, a backing paper or continuous web material is coated by roll coating with a release layer. This release layer is usually a silicone-based polymer. A removable and/or permanent pressure-sensitive adhesive is applied to the exposed surface of the release layer in a manner similar to that used for the release layer. This adhesive is typically a permanent and/or removable pressure-sensitive adhesive. Finally, face stock is applied to the exposed surface of the pressure-sensitive adhesive. The label may be printed or otherwise decorated by silkscreening or other conventional printing techniques on the face stock. This label stock material can be in either sheet or roll form. In some instances, the labels are die-cut with undesired matrix material removed.
The inability to easily and quickly detect imperfectly formed die-cut patterns is an old problem. This situation is particularly troublesome when white backing paper is used with white face stock to produce labels and/or signage, or more broadly stated, when similarly colored facestock is applied to similarly colored backing paper, and additionally, in the situation where there is transparent facestock with lettering of a similar coloration to the backing paper. When letters, particularly those with closed areas, such as the letter O, or letter A, or punctuation marks, are die-cut and the undesired matrix removed from the face stock, it is difficult to determine the quality of the die-cut with a similar color scheme of face stock and backing paper. A color contrast would be most desirable between the die-cut face stock and the backing material.
Prior art solutions to this problem have included coloration of the backing paper. While this may be effective in some instances, many production lines are geared toward using backing material with certain processing characteristics and the colorant employed in the backing paper can adversely affect these characteristics. Additionally, many label manufacturers do not wish to change their backing paper suppliers for reasons such as cost, long-term contract, quality, etc.
In U.S. Pat. No. 4,716,052 to Waugh et al., the adhesive layer was colored to provide a background for information or indicia printed thereon. The purpose of this coloration though was for decorative purposes only, and could not solve the problem of identifying improperly die-cut labels as the adhesive is removed with the undesired matrix.
The coloration of the polysiloxane polymer release coating is an alternative to coloring the backing material. Until now, however, there has been no effective means for coloring this layer without significantly affecting the release characteristics of the polysilane polymer release coating, the characteristics of the pressure-sensitive adhesive as it releases from the release coating, and/or the migration of the colorant into the pressure-sensitive adhesive to degrade the adhesive properties.